Three-dimensional porous polyurea networks and methods of manufacture

Abstract

Porous three-dimensional networks of polyurea and porous three-dimensional networks of carbon and methods of their manufacture are described. In an example, polyurea aerogels are prepared by mixing an triisocyanate with water and a triethylamine to form a sol-gel material and supercritically drying the sol-gel material to form the polyurea aerogel. Subjecting the polyurea aerogel to a step of pyrolysis may result in a three dimensional network having a carbon skeleton, yielding a carbon aerogel. The density and morphology of polyurea aerogels can be controlled by varying the amount of isocyanate monomer in the initial reaction mixture. A lower density in the aerogel gives rise to a fibrous morphology, whereas a greater density in the aerogel results in a particulate morphology. Polyurea aerogels described herein may also exhibit a reduced flammability.

What is claimed is: 
     
       1. A method of manufacturing an aerogel monolith, the method comprising:
 mixing an isocyanate, water, and a catalyst in a solvent to cause conversion of isocyanate groups on the isocyanate into in situ formed amine groups, and resulting in polymerization of the in situ formed amine groups and remaining unreacted isocyanate groups to form a sol-gel material comprising polyurea; and 
 drying the sol-gel material to form the aerogel monolith comprising polyurea, 
 wherein the aerogel monolith has a skeletal density of from 1.15 g/cm 3  to 1.32 g/cm 3 . 
 
     
     
       2. The method of  claim 1 , wherein the isocyanate is a triisocyanate or a diisocyanate. 
     
     
       3. The method of  claim 1 , wherein the catalyst is a trialkylamine. 
     
     
       4. The method of  claim 1 , further comprising agitating a mixture of the isocyanate, the water, and the catalyst to form the sol-gel material. 
     
     
       5. The method of  claim 1 , wherein the aerogel monolith is a variable density polyurea aerogel monolith. 
     
     
       6. The method of  claim 1 , wherein drying the sol-gel material comprises supercritically drying the sol-gel material. 
     
     
       7. The method of  claim 1 , wherein drying the sol-gel material comprises subcritically drying the sol-gel material. 
     
     
       8. The method of  claim 1 , wherein the solvent comprises acetone and/or DMSO. 
     
     
       9. The method of  claim 1 , wherein drying the sol-gel material comprises drying the sol-gel material to form a polyurea aerogel monolith, wherein mixing an increasing amount of the isocyanate to form the sol-gel material gives rise to an increasing density in the polyurea aerogel monolith. 
     
     
       10. The method of  claim 9 , wherein mixing a decreasing amount of the isocyanate to form the sol-gel material gives rise to a decreasing density in the polyurea aerogel monolith. 
     
     
       11. The method of  claim 1 , wherein drying the sol-gel material comprises
 drying the sol-gel material to form a polyurea aerogel monolith, wherein mixing a decreasing amount of the isocyanate to form the sol-gel material gives rise to an increasingly fibrous morphology in the polyurea aerogel monolith. 
 
     
     
       12. The method of  claim 11 , wherein mixing an increasing amount of the isocyanate to form the sol-gel material gives rise to an increasingly particulate morphology in the polyurea aerogel monolith. 
     
     
       13. The method of  claim 1 , wherein the aerogel monolith comprises a fibrous aerogel monolith having fibrous morphology and a density of less than about 900 mg/cc. 
     
     
       14. The method of  claim 13 , wherein the aerogel monolith comprises an insulator, a structural material, and/or an impact dampening material. 
     
     
       15. The method of  claim 1 , wherein the aerogel monolith has a density of less than about 150 mg/cc. 
     
     
       16. The method of  claim 1 , wherein the aerogel monolith has a density of greater than about 150 mg/cc. 
     
     
       17. The method of  claim 16 , wherein the aerogel monolith has a particulate morphology. 
     
     
       18. The method of  claim 1 , further comprising pyrolyzing the aerogel monolith to form a carbon aerogel. 
     
     
       19. The method of  claim 18 , further comprising agitating the mixture of the isocyanate, the water, and the catalyst to form the sol-gel material. 
     
     
       20. The method of  claim 15 , wherein the aerogel monolith has a density of less than about 90 mg/cc. 
     
     
       21. The method of  claim 1 , further comprising causing the isocyanate and water to react to form an isocyanate-derived amine and carbon dioxide. 
     
     
       22. The method of  claim 21 , further comprising causing the isocyanate and isocyanate-derived amine to react to form urea. 
     
     
       23. The method of  claim 1 , wherein the aerogel monolith consists essentially of polyurea. 
     
     
       24. The method of  claim 3 , wherein the trialkylamine comprises at least one of trimethylamine, triethylamine, tributylamine, and tripentylamine.